One of the newest,
and most promising, developments in polymer science is the emergence of
bioplastics. Bioplastics are polymers made completely, or at least partially,
from renewable resources like cellulose, starch, and algae. It is widely
believed that increasing acceptance of bioplastics will help slow the pace of
climate degradation by reducing dependence on fossil fuels. The market for
bioplastics is accelerating rapidly and industry experts believe it could reach
$3 billion by 2018.
Pyrolysis-GCMS has
long played a role in the study of industrial polymers such as rubbers,
coatings, and plastics. The technique is admired for both qualitative and
quantitative effectiveness when used to identify and understand unknown polymers
and additives. This familiar, tested technology is now being used to assist in
the identification of unknown bioplastics, as well as research targeting new
materials. Analytical pyrolysis of these newer plastics can reveal their true
makeup.
A common biopolymer
is polylactic acid (PLA), a plastic made from cornstarch. When this plastic is
pyrolyzed, you will get a prominent peak for PLA's dimer (lactide). Another
example is Polyhydroxybutyrate
(PHB), which is made by bacteria. When this biopolymer is pyrolyzed, the
main peak produced that we can use for identification is butenoic acid.
As would be expected, depending
on sample complexity, not all biopolymers are as easy to identify. However, with some of the recent advances in
pyrolysis instruments and polymer identification libraries, it is now possible
to identify trace level additives and polymers in the most complex
multi-polymeric samples. Some newer
pyrolyzer systems have the ability to heat a given sample at multiple
temperatures, making it possible to "thermally cut" analytical results into
simpler, less complex runs.
The example shown here is from a
compostable plastic garbage bag run at three different temperatures, 150°C, 300°C
and 750°C. Results from the second run (300°C) show that a small amount of
lactide is produced indicating PLA, which is usually made from cornstarch. Having
the option of multiple-step runs made it possible to locate the lactide, hidden
under the large peak for benzoic acid in the 3
rd highest temperature
run. It can be detected here by extracting ion 56, but without seeing it in the
lower temperature (300°C) run first, it might easily have been missed. The last
pyrolysis run (750°C) also produces a large peak for benzoic acid, and another
peak for biphenyl. These are aromatics typical of polyesters containing
terephthalate. Butadiene is also present, so the combination of these pyrolysis
products could result from the compostable polyester, polybutylene
adipate/terephthalate, in addition to PLA seen in the second run (300°C).
CDS Analytical manufactures a full
product line of pyrolyzers and GCMS injection systems. We will be displaying our products at the
upcoming PITTCON, Analytica-Munich and Arab Lab conferences. You can also review our pyrolyzer line on our
web page at
http://www.cdsanalytical.com/instruments/pyrolysis/pyroprobe_5000.html .
For further application details
on pyrolysis of bioplastics or other polymer applications, please contact CDS
at
sales@cdsanalytical.com or call at +1 610 932
3636.
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